The present invention relates generally to cap closures and more particularly to an improved method and apparatus for applying a liner of plastisol material to unlined cap closures.
For many years the conventional bottle closure consisted of a metal cap which had a cork disk secured therein which would seal against the top of a package to seal the contents therein.
In more recent years substantial activity and development has occurred in the plastic field and the utilization of plastic as a lining material has become substantially standard in the industry, replacing the conventional cork liner.
Various types of apparatus for applying liners to unlined cap closures have been proposed and are in existence at the present time. One type of apparatus that has been used extensively is disclosed in Aichele U.S. Pat. No. 3,135,019. This patent discloses a machine for applying liners of thermoplastic material to cap closures, particularly crown caps. In the machine disclosed in this patent, the caps are preheated and a heated thermoplastic material in a soft plastic condition is fed in metered amounts to the respective unlined caps. The thermoplastic material is then shaped or molded and set into a liner formation by a molding head that is rotated in a continuous fashion. A specific type of plastic metering means for the above machine is disclosed in Aichele U.S. Pat. No. 3,212,131 which is capable of feeding small charges of thermoplastic material at rates of approximately 300 caps per minute.
Another type of crown cap lining machine is disclosed in Simpson U.S. Pat. No. 2,954,585 which contemplates depositing predetermined amounts of a thermosetting plastic lining material into unlined caps and transferring the caps with the uncured plastic to a molding and curing turret which has circumferentially spaced clamps into which the plastic container caps are fed and clamped therebetween. The clamping members coact to clamp the lined cap during which heat is applied to cure the cap liners and the cured lined caps are then discharged through a take-off mechanism associated with the turret.
More recently, a more acceptable type of lining material has been developed which is capable of producing small voids in the material as the liner is being formed in the cap closure. This type of lining material includes a plastisol material, fillers and waxes plus a blowing agent which is deposited into the unlined cap closures and is subsequently heated to cure the liquid lining compound. During the curing process, the blowing agents dissolve at a predetermined temperature and create small voids in the finished and cured lining material in the cap closure. It has been determined that the small voids aid in producing a proper seal with a container, such as a glass bottle, which in many instances has small nicks or uneven upper edges to which the cap closure must be sealed.
In producing lined cap closures utilizing the material which results in creating small voids, it has heretofore been customary in producing such lined cap closures to feed unlined caps into a feeding mechanism where a predetermined charge of liquid uncured lining compound is applied to each of the caps. The caps with the charge of compound therein are then fed to a molding head having a plurality of circumferentially spaced molding stations thereon wherein the charges of uncured material are molded to a final configuration and at least partially cured so that the lining material is set within the cap closure. The cap closures are then moved through an oven wherein the temperature of the caps and the lining materials is increased sufficiently to dissolve the blowing agents and fully cure the plastisol material.
One of the problems inherent with the system that has been in use for some time is the limitation of the speed at which the uncured lining material can be fed to the unlined caps before they are delivered to a molding machine. For years, a maximum speed at which such liquid lining compound could be dispensed to the unlined caps was on the order of 600 charges per minute. Most types of dispensing units that are presently in existence and have been used for dispensing such products consist of some type of plunger arrangement mounted within a chamber having a packing material surrounding the plunger and which is reciprocated through a pressurized fluid source, such as air. Since the liquid compound must be fed to the dispensing unit under pressure, a packing seal must be placed around the periphery of the plunger to prevent the compound from leaking through the dispensing unit. The heat that is developed from the friction between the movable plunger and the stationary chamber and packing seal many times results in curing the liquid lining compound before it is dispensed thereby necessitating a shutdown to remove the partially cured material. With such a cycling system, it is also difficult to substantially increase the speed for a machine in view of the complexity of being able to reverse the cycle of air substantially beyond 600 cycles per minute.